This invention relates to elastomeric compositions having improved tear strength and good processability.
Many industrially important elastomers have low tear strength and/or low cut growth resistance, which shortcomings decrease their utility in applications such as, for example, belts and tubing for automotive and other applications. It is known to increase the tensile strength and to improve the tear strength of various elastomers by the addition of polytetrafluoroethylene (PTFE) powder; see, for example, U.S. Pat. No. 3,940,455 to Kaufman and Japanese patent publication Kokai No. 57-10895 (1982) of Daikin Kogyo K.K.
Since, however, PTFE powder does not have good compatibility with most elastomers, including fluoroelastomers, it cannot be readily dispersed in an elastomer to give a uniform composition. Those prior art PTFE powder-containing elastomeric compositions usually had a non-uniform, blotchy appearance. In addition, their modulus was considerably increased, sometimes to the point where they were no longer processible in conventional equipment by normal techniques.
It is known from U.S. Pat. No. 2,871,144 to Doban to modify the surfaces of fluorocarbon polymer articles to improve their bondability by treating those surfaces with solutions of alkali metal additives with aromatic hydrocarbons. It also is known from Japanese Pat. No. 79/013467 to Sumitomo Electric Ind. K.K. to treat PTFE powder with sodium-naphthalene, to mix such treated powder with a lubricating liquid, and to extrude it into a sheet.
There has been no disclosure or suggestion, however, that treated PTFE powder could be dispersed in a variety of elastomeric materials to give uniform elastomeric compositions having improved tear strength and good processability.